A conventional vehicle door control system controls locking and unlocking of each door of a vehicle by way of bilateral communications between a portable unit (e.g., portable electronic key) and a vehicle unit and checking ID codes. In this system, transmitters of the vehicle unit periodically transmit request signals to define predetermined range of communications areas around the vehicle respectively. Thus, the system monitors approaching and leaving of a holder (e.g., vehicle driver) carrying the portable unit to and from the vehicle.
For example, when the holder approaches the vehicle and enters into the communications area to get in the vehicle, the portable unit transmits a response signal including its ID code in response to the received request signal. The vehicle unit receives the response signal and check whether the ID code included in the response signal matches a registered ID code stored in the vehicle unit, that is, whether the two ID codes are in a predetermined correspondence relation. If both IDs match, the vehicle unit generates a control signal to each door control device in the vehicle to drive the vehicle door to an unlock standby condition. When the holder touches a door handle under this standby condition, the vehicle door control device responsively opens the vehicle door.
In another conventional vehicle door control system, for example, US 2006/0214769 A1 (JP 2006-266023A), an automatic open/close door is automatically opened in response to the unlocking of the vehicle door. This automatic door-opening operation further enhances convenience for the holder having the portable unit.
However, the unlocking operation and the automatic door-opening operations are effected only when the holder performs a certain manipulation (unlock operation) on a door handle. Such a manipulation includes, for example, touching a door handle or manipulating a switch provided on the door handle. The door handle manipulation is required for the vehicle door unlocking and the automatic door opening to inhibit the vehicle door from being unlocked or automatically opened erroneously and unintendedly whenever the holder approaches close to the vehicle.
However, when the holder carries luggage such as boxes, packages or articles by both hands, it is difficult for him/her to perform the required unlock manipulation on the door handle. In this instance, the holder is obliged to place the luggage on the ground once and then takes up the same again after completing the required unlock manipulation on the door handle.